Field of Invention
The invention relates to a control method and a control system and, in particular, to a control method and a control system of a fan.
Related Art
A fan is commonly used for the heat dissipation. When a fan is applied to a client system, it usually will be increased or decreased in the number of blades according to the different requirements of the client system, and also the rotational speed of the fan will be controlled and driven by a control chip or apparatus, so that the rotational speed of the fan can be properly adjusted to fit the actual operation conditions of the client system.
FIG. 1 is a schematic diagram showing the architecture of a conventional fan. The fan in FIG. 1 is instanced as a DC brushless fan. The fan 1 includes a control system outputting four switch signals T1˜T4 to four switch elements 12 for switching the phase. The four switch elements 12 are connected to a coil of a motor 13. The control system 11 includes a control unit 111 and a comparator 112. The control unit 111 outputs a switch control signal to the comparator 112, and the comparator 112 compares the control signal and a triangle wave to output the switch signals T1˜T4. FIG. 2A is a schematic diagram of two waveforms of the conventional switch control signal, and FIG. 2B is a schematic diagram of the conventional switch signals. Conventionally, the common driving method of the fan is hard-switching method which is shown by the switch control signal V1 in FIG. 2A. However, the hard-switching method easily causes larger vibrations. Therefore, in order to reduce vibrations, another driving method, i.e. soft-switching method, is used, which is shown by the switch control signal V2 in FIG. 2A. In FIG. 2B, the switch signals T1˜T4 are generated according to the switch control signal V2 of the soft-switching method. The regions a in FIG. 2B denote the portion of the soft-switching.
FIG. 3 is a schematic diagram of a vibration spectrum of a conventional fan, wherein the abscissa axis represents the frequency of the rotational speed while the ordinate axis represents the amount of the vibration. FIG. 3 is obtained by transforming the vibration of the fan with a Fourier transform, and the vibration level can be known from FIG. 3. From FIG. 3, it can be seen that the largest vibration level of the conventional fan is larger than 1.5G, and therefore the vibration amount can not be effectively decreased even if the soft-switching method is used to drive the fan.
Otherwise, mechanism design is mostly used for solving the vibration problem of the fan. For the mechanism design, for example, several anti-vibration pads can be added or the mechanical resonance point can be changed to reduce the vibration. However, the frequency multiplication effect caused by the motor can not be overcome by the mechanism design. Besides, the mechanism design will increase the cost and also can not effectively solve the vibration problem.
Therefore, it is an important subject to provide a control method and a control system of a fan that can decrease the fan's vibration under the current driving circuit and architecture for enhancing the efficiency and decreasing the electric pressure.